Intake of excessive nutrients induces secretion of a larger amount of insulin to indirectly cause a collapse of metabolic balance, thus leading to a reduction of glucose tolerating function (hyperglycemia), diabetes, hyperlipemia, arteriosclerosis, etc. Especially in diabetic patients, the insulin function is insufficient and the glucose tolerance is lowered. Consequently the blood glucose level is remarkably increased after meals, thereby causing complications such as damage to blood capillaries and arteriosclerosis. For the prevention and treatment of such diseases it is effective to ingest foods or materials which can hardly induce an increase in blood glucose level. In this respect materials capable of inhibiting or preventing hydrolysis of starch into glucose have been desired. Further, overeating contributes to diseases of adult people such as adiposity, hypertension, diabetes and cardiac diseases.
From the above aspects, various studies have been made on so-called amylase inhibitors which are effective in inhibiting the activity of amylase to hydrolyze starch. It is reported that amylase inhibitors are also contained in wheat. Since then, amylase inhibitors of wheat origin have been investigated [see, for example, U.S. Pat. No. 3,950,319, Japanese Patent Kokai 61-171431, Phytochemistry, vol. 20, No. 8, pp. 1781-1784, 1981; Eur. J. Biochem. 183, 37-40 (1989)].
However, it is reported that prior amylase inhibitors of wheat origin as mentioned above have exceedingly low or no inhibitory activity against human pancreatic .alpha.-amylase, and do not produce an effect as expected when orally given to humans, although they have some inhibitory activity against amylases of other animals than human. Therefore, there is a need for a highly active amylase inhibitor having a strong inhibitory activity against human pancreatic .alpha.-amylase and capable of effectively inhibiting an increase in blood glucose level and insulin secretion when orally administered at a low level, especially capable of effectively inhibiting hydrolysis of heated or cooked starch.
Further it is reported that an agent for inhibiting an increase in blood glucose level or insulin secretion brings about an increased level of free fatty acids in blood [Puls and Keup, "Diabetologia" 9, 97-101 (1973)]. In general, such increased levels bring about the feeling of hunger which will lead to overeating. This results in offsetting the effect of inhibiting an increase in blood glucose level and the effect of inhibiting an insulin secretion, which will make it difficult to effectively treat or prevent the diseases such as diabetes.